1. Field of the Invention
The present invention relates to an optically functional layer comprising a cured product of polymerizable liquid crystal composition by polymerization such as an optical retardation control layer, a color filter layer, a polarizing control layer or the like, which is particularly suitable for applying to various displays, notably, a liquid crystal display.
The present invention also relates to a method of forming the optically functional layer, and a liquid crystal display element using the optically functional layer.
2. Description of the Related Art
In order to form an optically functional layer such as the above mentioned optical retardation control layer or the like using a polymerizable liquid crystal composition, it is necessary to employ a method comprising steps of applying a polymerizable liquid crystal composition on a substrate and subjecting the applied substrate to exposure to cure the composition by polymerization. It is also necessary to use a photopolymerization initiator to initiate radical reaction with the exposure light. For example, benzil dimethyl ketal based 2,2-dimethoxy-1,2-diphenylethane-1-one (manufactured by Chiba Specialty Chemicals, Inc.; product name: Irgacure 651) may be used (for example, Kohyo (Japanese Unexamined Patent Publication) No. 2001-500984, p. 21). Alternatively, besides the above mentioned, α-hydroxyketone based 1-hydroxy-cyclohexyl-phenyl-ketone (manufactured by Chiba Specialty Chemicals, Inc.; product name: Irgacure 184), α-hydroxyketone based 2-hydroxy-2-methyl-1-phenyl-propane-1-one (manufactured by Merck & Co., Inc.; product name: Darocure 1173), or Darocure 4205 (product name; manufactured by Merck & Co., Inc.; composition unknown) may be used (for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-56484, p. 15).
However, the heat resistance of the optically functional layers obtained by using any of the above photopolymerization initiators was not necessarily sufficient.
Particularly, there was a risk of deteriorating a display quality level as impurity elutes into a liquid crystal layer when an optical retardation control layer comes into contact with the liquid crystal layer because of the insufficient heat resistance of the optical retardation control layer leading to the deterioration in the optical retardation control layer due to high temperature of processing after forming the optical retardation control layer, the insufficient chemical resistance of the obtained optical retardation control layer, or the like.